Cleaning Foggy Double-Pane Windows


Sharolyn asked: How do I clean a double pane patio door? We recently placed an old camper on the back of our property, in the woods, to enjoy on weekends. The patio door has become so foggy on one section that we cannot see through it. We do not care if it is sealed or now, but would like to be able to sit inside and see out. How can we get to the inside of the door to clean it?

Double pane doors and windows consist of two panes of glass with a space between them. This bit of insulating air space increases the R value of the window, but it’s also prone to fogging, especially in older units or ones that withstand a lot of abuse from the elements. Fogging results when the seal fails or is compromised in any way, allowing moisture to seep through the barrier and into the space between the glass. Seal failure can occur with too much heat (when the seal softens and expands) or in cold temperatures (when it hardens and becomes brittle).

Once the seals fail and fogging begins, there’s no practical way to repair it. Theoretically, you would have to separate the panes of glass, clean and thoroughly remove all moisture, then reattach and seal them. Doing so without trapping any humidity is improbable, if not impossible, and then you need to replicate a factory-quality seal without breaking or damaging the glass. Therefore, the only effective way to rid your view of the fogging is to replace the door.

If you opt to remove the seal to clean the door, be aware that the problem will quickly reoccur. While the initial cleaning will remove the dirt temporarily, the lack of a seal will cause the door to fog over and collect dirt much quicker. Some say to remove one of the panes so that it becomes a single-pane door. However, the fixtures are not designed for this and the single pane will fit loosely in the fixture. This makes it more prone to breaking and damage.

If you choose to remove the panes and the seal for cleaning, consult your owner’s manual or manufacturer for the proper method to remove the glass panes. All doors are designed differently, and the disassembly steps are not the same for each door type. Still, consider replacing the door with a low-cost single pane door, and you will have both a better view and stronger fixture.

Newer technology has reduced the failure rate of properly installed double pane doors to 1% after 10 years and 3% after 15 years, so your investment should be a lasting one. To increase the lifetime of your new double pane doors, keep the following in mind:

  • Purchase glass with a long warranty. This generally means a higher quality product, and if not, a premature failure is a covered repair.
  • Inspect your glass periodically. Look for the seals to be in good shape. Any splits, cracks, or other deterioration is a warning sign that failure, and condensation or fogging, may be in your future.
  • Keep glass clean and ensure good circulation around it. If dirt and moisture are allowed to build and remain on the outer surfaces, they will wear away at the seals and may speed up the process of failure.


  1. Billy Bob says:

    There is one way to do this, but it is hardly worth the trouble and it requires certain special equipment and some aptitude with tools and repair work. You first need to determine if you can take the door frame apart and access the double pane glass section of the door under the frame. This may or may not be feasible. If you can pull the frame or at least one side of the frame away from the glass, then this is a start. The glass panes will be like a sandwich with what is usually a butyl rubber or similar type gasket all around their perimeter. You will need to drill two small holes smaller than the gap between the glass panes. The bigger the hole, the better; usually 1/4 inch will suffice. Each hole should be 2 to 3 inches from the corners on each end you are working on. Drill slowly and carefully. After you get the holes drilled, you need to use denatured alcohol; you can buy it in the paint department of a hardware store. Using a funnel and some plumbers putty, line the funnel over the hole, sealing it with the putty. Pour the denatured alcohol into the hole and put enough between the glass to slosh around and clean it. Now, dump the alcohol out of the glass; the second hole helps by letting air in to displace the alcohol. Now, the tricky part. Acquire a vacuum pump; these are not cheap. Borrow one from a friend or rent one from a rental store. You can buy a small one at harbor freight for $100. You will need to fashion a connection between the vacuum pump and one of the small holes you drilled in the butyl rubber gasket. This will probably require some stiff 1/4 inch tubing and a stepped fitting to fit in the gasket hole. Before you pull the vacuum on the glass sandwich, you should put a bead of silicone caulk all the way around the gasket to seal whatever leak was letting in air in the first place. Spread the bead evenly with your finger to seal over the rubber gasket. Allow this to dry completely. Now, plug one of the two holes you drilled in the gasket and seal it shut. Now, put the stepped fitting in the only remaining hole and turn on the vacuum pump. Watch the gauge on the pump and stop the pump when the gauge reaches about -10. Most pumps can pull a vacuum down to about 26 – 28; good ones can pull down to 30 atmospheres…this would probably suck in the gasket and destroy the glass sandwich or break the glass. Now, since you have removed all the air, you can quickly use a plug and seal the hole you used to vacuum out the window. Seal the plug with silicone caulk; let dry. Reattach door frame to window. Viola!

  2. In reply to Billy Bob… Pulling a vacuum on ANY large area of unsupported glass will almost certainly result in catastrophic failure of the glass. Even a slight vacuum will cause the panes to over-stress and implode. Let’s say you’ve put a very small 1 PSI vacuum in the space. That’s a 1/15th reduction of the atmosphere (what you are feeling right now if you are sitting on the beach). Not much of a vacuum. This vacuum would hardly be enough to remove the moisture of the air, but let’s look at the pressures the glass would experience.
    On a 23″X66″ panel (approximately standard commercial fridge door), we would calculate the total force as 23X66X1 = 1518 pounds of pressure on each opposing pane of glass. That’s a recipe for disaster. To remove the air effectively enough, you would need at least a 9 PSI vacuum or 13662 surface pressure to do so. Not possible. Don’t vacuum out your panes.
    The industry uses a different technique to effectively remove the humidity. Firstly, they do as Billy has stated and put two small holes in the seal; one for injection and one for pressure relief. They then drift dry nitrogen through the panel for several minutes to remove the air and humidity. As a final step, they slowly drift argon gas into the space, which is heavier than nitrogen and thusly forces the nitrogen out through the vent hole. After all of the space is filled with argon, the holes are sealed. The argon acts as an insulator and gives excellent thermal insulation, and because it’s dry, the glass pane won’t fog up. The thermal expansion and contraction of argon is extremely minimal, and upon heat or cooling, won’t cause the panes to crack from over/under pressuring the area between the panes.
    Hope this helps.

  3. Has anyone tried sealing the two glass panels back together with silicone while working in a very small space while running a dehumidifier for a time to get the relative humidity down to 30 % or less, then seal the two glass panels?? Capture that dry air…?

  4. Glass Fiend says:

    1- If you don’t have access to the edge of the sealed unit to drill, you can drill the surface of the glass using a cheap diamond bit (see eBay). Make a hole that is 1/4″ to 1/2″.

    2- After washing the inside of the glass (alcohol, vinegar, Windex, etc.), get an electric air pump, connect it by a tube, and blow dry the inside by blowing air for a few days. Make sure all water in the aluminum spacers is removed.

    3- Get colored moisture desiccant (eBay) and cook it on low temperature until it is a vivid blue and dry. Pour the desiccant in the holes drilled, and immediately seal all holes with silicone and clear plastic on top of the silicone. If the desiccant turns purple, then remove it and put in more blue desiccant.

    This will work if the leak in the seal is very minor. But, if the leak is major, the desiccant can’t help. Might as well open up all the drilled holes and let the sealed unit vent itself and stay dry. On cold days, you may see condensation.

    The insulation value drops, but not by a lot.

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